Method of performing a qualification action on an exposure apparatus

Abstract

Disclosed is a method of method of performing a qualification action relating to an exposure apparatus. The method comprises: using the exposure apparatus to expose a qualification patterning device (400) onto at least one qualification substrate, the qualification patterning device (400) comprising one or more sets of metrology features (410) which comprise one or more overlay features (445) and one or more imaging features (440), the overlay (445) and imaging features (440) being in close proximity; measuring the at least one qualification substrate to obtain qualification data comprising at least overlay qualification data and imaging qualification data; determining at least one local structure placement metric from said at least overlay qualification data and imaging qualification data; and qualifying said exposure apparatus by assessing said local structure placement metric.

Description

METHOD OF PERFORMING A QUALIFICATION ACTION ON AN EXPOSURE APPARATUSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 24184876.1 which was filed on June 27, 2024 and which is incorporated herein in its entirety by reference.BACKGROUND

[0002] The present invention relates to methods and apparatus usable, for example, in the manufacture of devices by lithographic techniques, and to methods of manufacturing devices using lithographic techniques.FIELD OF THE INVENTION

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of a die, one die, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. These target portions are commonly referred to as “fields”.

[0004] In the manufacture of complex devices, typically many lithographic patterning steps are performed, thereby forming functional features in successive layers on the substrate. A critical aspect of performance of the lithographic apparatus is therefore the ability to place the applied pattern correctly and accurately in relation to features laid down (by the same apparatus or a different lithographic apparatus) in previous layers. For this purpose, the substrate is provided with one or more sets of alignment marks. Each mark is a structure whose position can be measured at a later time using a position sensor, typically an optical position sensor. The lithographic apparatus includes one or more alignment sensors by which positions of marks on a substrate can be measured accurately. Different types of marks and different types of alignment sensors are known from different manufacturers and different products of the same manufacturer.

[0005] In other applications, metrology sensors are used for measuring exposed structures on a substrate (either in resist and / or after etch). A fast and non-invasive form of specialized inspection tool is a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured. Examples of known scatterometers include angle-resolved scatterometers of the type described in US2006033921A1 and US2010201963Al. In addition to measurement of feature shapes by reconstruction, diffraction basedoverlay can be measured using such apparatus, as described in published patent application US2006066855A1. Diffraction-based overlay metrology using dark-field imaging of the diffraction orders enables overlay measurements on smaller targets. Examples of dark field imaging metrology can be found in international patent applications WO 2009 / 078708 and WO 2009 / 106279 which documents are hereby incorporated by reference in their entirety. Further developments of the technique have been described in published patent publications US20110027704A,US20110043791A, US2011102753A1, US20120044470A, US20120123581A, US20130258310A, US20130271740A and WO2013178422A1. These targets can be smaller than the illumination spot and may be surrounded by product structures on a wafer. Multiple gratings can be measured in one image, using a composite grating target. The contents of all these applications are also incorporated herein by reference.

[0006] It is necessary to routinely qualify or assess performance of a tool, for example prior to delivery or when a tool is first installed or delivered (or possibly after a maintenance action). The performance is typically measured in terms of five key performance metrics: focus, imaging, defectivity, overlay and productivity. This is typically assessed by testing for each of these performance metrics in turn.

[0007] It is desirable to improve on such qualification actions.SUMMARY OF THE INVENTION

[0008] The invention in a first aspect provides a method of performing a qualification action relating to an exposure apparatus, the method comprising: using the exposure apparatus to expose a qualification patterning device onto at least one qualification substrate, the qualification patterning device comprising one or more sets of metrology features, the one or more sets of metrology features comprising one or more overlay features for forming one or more overlay structures on the qualification substrate for the measurement of overlay and one or more imaging features for forming one or more imaging structures on the qualification substrate for the measurement of at least one imaging parameter, wherein, for each of the one or more sets of metrology structures, at least one of said one or more overlay structures is, on the qualification substrate, within 2.5mm of at least one of said one or more imaging structures; measuring the at least one qualification substrate to obtain qualification data comprising at least overlay qualification data relating to overlay and imaging qualification data relating to the at least one imaging parameter; determining at least one local structure placement metric from said at least overlay qualification data and imaging qualification data; and qualifying said exposure apparatus by assessing said local structure placement metric.

[0009] The invention in a second aspect provides a qualification patterning device for qualifying an exposure apparatus, comprising: a plurality of sets of metrology features, each of the plurality of sets of metrology features comprising one or more overlay features for forming one or more overlay structures on the qualification substrate for the measurement of overlay and one or more imagingfeatures for forming one or more imaging structures on the qualification substrate for the measurement of at least one imaging parameter, wherein, for each of said one or more sets of metrology features, at least one of said one or more overlay features is, on the reticle, within 10mm of at least one of said one or more imaging features; and representative product features for forming representative product structures being representative of product structures of a particular application and / or use case for said exposure apparatus.

[0010] The above and other aspects of the invention will be understood from a consideration of the examples described below.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0012] Figure 1 depicts a lithographic apparatus; and

[0013] Figure 2 illustrates schematically measurement and exposure processes in the apparatus of Figure 1;

[0014] Figures 3(a) and 3(b) comprise (a) a schematic diagram of a dark field scatterometer for use in measuring targets according to embodiments of the invention using a first pair of illumination apertures and (b) a detail of diffraction spectrum of a target grating for a given direction of illumination; and

[0015] Figure 4 illustrates a qualification reticle usable in methods according to concepts disclosed herein.DETAILED DESCRIPTION OF EMBODIMENTS

[0016] Before describing embodiments of the invention in detail, it is instructive to present an example environment in which embodiments of the present invention may be implemented.

[0017] Figure 1 schematically depicts an exposure apparatus or lithographic apparatus LA. The apparatus includes an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., UV radiation or DUV radiation), a patterning device support or support structure (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; two substrate tables (e.g., a wafer table) WTa and WTb each constructed to hold a substrate (e g., a resist coated wafer) W and each connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g., including one or more dies) of the substrate W. A reference frame RF connects the various components, and serves as a reference for setting and measuring positions of the patterning device and substrate and of features on them.

[0018] The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.

[0019] The patterning device support MT holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The patterning device support can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The patterning device support MT may be a frame or a table, for example, which may be fixed or movable as required. The patterning device support may ensure that the patterning device is at a desired position, for example with respect to the projection system.

[0020] The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.

[0021] As here depicted, the apparatus is of a transmissive type (e.g., employing a transmissive patterning device). Alternatively, the apparatus may be of a reflective type (e.g., employing a programmable mirror array of a type as referred to above, or employing a reflective mask). Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.” The term “patterning device” can also be interpreted as referring to a device storing in digital form pattern information for use in controlling such a programmable patterning device.

[0022] The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”.

[0023] The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems.

[0024] In operation, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD including, for example, suitable directing mirrors and / or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

[0025] The illuminator IL may for example include an adjuster AD for adjusting the angular intensity distribution of the radiation beam, an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross section.

[0026] The radiation beam B is incident on the patterning device MA, which is held on the patterning device support MT, and is patterned by the patterning device. Having traversed the patterning device (e.g., mask) MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g., an interferometric device, linear encoder, 2-D encoder or capacitive sensor), the substrate table WTa or WTb can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in Figure 1) can be used to accurately position the patterning device (e.g., mask) MA with respect to the path of the radiation beam B, e.g., after mechanical retrieval from a mask library, or during a scan.

[0027] The lithographic apparatus may comprise an aberration sensor for the verification of an aberration fingerprint of the projection system PS. In an embodiment such an aberration fingerprint, i.e. aberrations per field point of the projection system PS, may be determined using a such wavefront aberration sensor. A wavefront aberration sensor of a known type, for instance such as described in US2002 / 0001088 may be used. Such a wavefront aberration sensor may be based on the principle of shearing interferometry and comprises a source module and a sensor module. The source module may comprise a patterned layer of chromium that is placed in the object plane (i.e. where during production the pattern of the patterning means is) of the projection system PS and has additional optics provided above the chromium layer. The combination provides a wavefront of radiation to the entire pupil of the projection system PS. The sensor module may comprise a patterned layer of chromium that is placed in the image plane of the projection system (i.e. where during production the substrate W is) and a camera that is placed some distance behind said layer of chromium. The patterned layer of chromium on the sensor module diffracts radiation into several diffraction orders that interfere with each other giving rise to an interferogram. The interferogram is measured by the camera. The aberrations in the projection lens can be determined by software based upon themeasured interferogram. The wavefront aberration sensor may be configured to transfer information with respect to the aberration fingerprint towards the control unit.

[0028] Patterning device (e.g., mask) MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device (e g., mask) MA, the mask alignment marks may be located between the dies. Small alignment marks may also be included within dies, in amongst the device features, in which case it is desirable that the markers be as small as possible and not require any different imaging or process conditions than adjacent features. The alignment system, which detects the alignment markers is described further below.

[0029] The depicted apparatus could be used in a variety of modes. In a scan mode, the patterning device support (e.g., mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e., a single dynamic exposure). The speed and direction of the substrate table WT relative to the patterning device support (e.g., mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. Other types of lithographic apparatus and modes of operation are possible, as is well-known in the art. For example, a step mode is known. In so-called “maskless” lithography, a programmable patterning device is held stationary but with a changing pattern, and the substrate table WT is moved or scanned.

[0030] Combinations and / or variations on the above described modes of use or entirely different modes of use may also be employed.

[0031] Lithographic apparatus LA is of a so-called dual stage type which has two substrate tables WTa, WTb and two stations - an exposure station EXP and a measurement station MEA - between which the substrate tables can be exchanged. While one substrate on one substrate table is being exposed at the exposure station, another substrate can be loaded onto the other substrate table at the measurement station and various preparatory steps carried out. This enables a substantial increase in the throughput of the apparatus. The preparatory steps may include mapping the surface height contours of the substrate using a level sensor LS and measuring the position of alignment markers on the substrate using an alignment sensor AS. If the position sensor IF is not capable of measuring the position of the substrate table while it is at the measurement station as well as at the exposure station, a second position sensor may be provided to enable the positions of the substrate table to be tracked at both stations, relative to reference frame RF. Other arrangements are known and usable instead of the dual-stage arrangement shown. For example, other lithographic apparatuses are known in which asubstrate table and a measurement table are provided. These are docked together when performing preparatory measurements, and then undocked while the substrate table undergoes exposure.

[0032] Figure 2 illustrates the steps to expose target portions (e.g. dies) on a substrate W in the dual stage apparatus of Figure 1. On the left hand side within a dotted box are steps performed at a measurement station MEA, while the right hand side shows steps performed at the exposure station EXP. From time to time, one of the substrate tables WTa, WTb will be at the exposure station, while the other is at the measurement station, as described above. For the purposes of this description, it is assumed that a substrate W has already been loaded into the exposure station. At step 200, a new substrate W’ is loaded to the apparatus by a mechanism not shown. These two substrates are processed in parallel in order to increase the throughput of the lithographic apparatus.

[0033] Referring initially to the newly-loaded substrate W’, this may be a previously unprocessed substrate, prepared with a new photo resist for first time exposure in the apparatus. In general, however, the lithography process described will be merely one step in a series of exposure and processing steps, so that substrate W’ has been through this apparatus and / or other lithography apparatuses, several times already, and may have subsequent processes to undergo as well.Particularly for the problem of improving overlay performance, the task is to ensure that new patterns are applied in exactly the correct position on a substrate that has already been subjected to one or more cycles of patterning and processing. These processing steps progressively introduce distortions in the substrate that must be measured and corrected for, to achieve satisfactory overlay performance.

[0034] The previous and / or subsequent patterning step may be performed in other lithography apparatuses, as just mentioned, and may even be performed in different types of lithography apparatus. For example, some layers in the device manufacturing process which are very demanding in parameters such as resolution and overlay may be performed in a more advanced lithography tool than other layers that are less demanding. Therefore some layers may be exposed in an immersion type lithography tool, while others are exposed in a ‘dry’ tool. Some layers may be exposed in a tool working at DUV wavelengths, while others are exposed using EUV wavelength radiation.

[0035] At 202, alignment measurements using the substrate marks Pl etc. and image sensors (not shown) are used to measure and record alignment of the substrate relative to substrate table WTa / WTb. In addition, several alignment marks across the substrate W’ will be measured using alignment sensor AS. These measurements are used in one embodiment to establish a “wafer grid”, which maps very accurately the distribution of marks across the substrate, including any distortion relative to a nominal rectangular grid.

[0036] At step 204, a map of wafer height (Z) against X-Y position is measured also using the level sensor LS. Conventionally, the height map is used only to achieve accurate focusing of the exposed pattern. It may be used for other purposes in addition.

[0037] When substrate W’ was loaded, recipe data 206 were received, defining the exposures to be performed, and also properties of the wafer and the patterns previously made and to be made upon it.To these recipe data are added the measurements of wafer position, wafer grid and height map that were made at 202, 204, so that a complete set of recipe and measurement data 208 can be passed to the exposure station EXP. The measurements of alignment data for example comprise X and Y positions of alignment targets formed in a fixed or nominally fixed relationship to the product patterns that are the product of the lithographic process. These alignment data, taken just before exposure, are used to generate an alignment model with parameters that fit the model to the data. These parameters and the alignment model will be used during the exposure operation to correct positions of patterns applied in the current lithographic step. The model in use interpolates positional deviations between the measured positions. A conventional alignment model might comprise four, five or six parameters, together defining translation, rotation and scaling of the ‘ideal’ grid, in different dimensions. Advanced models are known that use more parameters.

[0038] At 210, wafers W’ and W are swapped, so that the measured substrate W’ becomes the substrate W entering the exposure station EXP. In the example apparatus of Figure 1, this swapping is performed by exchanging the supports WTa and WTb within the apparatus, so that the substrates W, W’ remain accurately clamped and positioned on those supports, to preserve relative alignment between the substrate tables and substrates themselves. Accordingly, once the tables have been swapped, determining the relative position between projection system PS and substrate table WTb (formerly WTa) is all that is necessary to make use of the measurement information 202, 204 for the substrate W (formerly W’) in control of the exposure steps. At step 212, reticle alignment is performed using the mask alignment marks Ml, M2. In steps 214, 216, 218, scanning motions and radiation pulses are applied at successive target locations across the substrate W, in order to complete the exposure of a number of patterns.

[0039] By using the alignment data and height map obtained at the measuring station in the performance of the exposure steps, these patterns are accurately aligned with respect to the desired locations, and, in particular, with respect to features previously laid down on the same substrate. The exposed substrate, now labeled W” is unloaded from the apparatus at step 220, to undergo etching or other processes, in accordance with the exposed pattern.

[0040] The skilled person will know that the above description is a simplified overview of a number of very detailed steps involved in one example of a real manufacturing situation. For example rather than measuring alignment in a single pass, often there will be separate phases of coarse and fine measurement, using the same or different marks. The coarse and / or fine alignment measurement steps can be performed before or after the height measurement, or interleaved.

[0041] Figure 3(a) presents an embodiment of a metrology apparatus and, more specifically, a dark field scatterometer. A target T and diffracted rays of measurement radiation used to illuminate the target are illustrated in more detail in Figure 3(b). The metrology apparatus illustrated is of a type known as a dark field metrology apparatus. The metrology apparatus may be a stand-alone device or incorporated in either the lithographic apparatus LA, e.g., at the measurement station, or thelithographic cell LC. An optical axis, which has several branches throughout the apparatus, is represented by a dotted line O. In this apparatus, light emitted by source 11 (e.g., a xenon lamp) is directed onto substrate W via a beam splitter 15 by an optical system comprising lenses 12, 14 and objective lens 16. These lenses are arranged in a double sequence of a 4F arrangement. A different lens arrangement can be used, provided that it still provides a substrate image onto a detector, and simultaneously allows for access of an intermediate pupil-plane for spatial-frequency filtering. Therefore, the angular range at which the radiation is incident on the substrate can be selected by defining a spatial intensity distribution in a plane that presents the spatial spectrum of the substrate plane, here referred to as a (conjugate) pupil plane. In particular, this can be done by inserting an aperture plate 13 of suitable form between lenses 12 and 14, in a plane which is a back-projected image of the objective lens pupil plane. In the example illustrated, aperture plate 13 has different forms, labeled 13N and 13S, allowing different illumination modes to be selected. The illumination system in the present examples forms an off-axis illumination mode. In the first illumination mode, aperture plate 13N provides off-axis from a direction designated, for the sake of description only, as ‘north’. In a second illumination mode, aperture plate 13S is used to provide similar illumination, but from an opposite direction, labeled ‘south’. Other modes of illumination are possible by using different apertures. The rest of the pupil plane is desirably dark as any unnecessary light outside the desired illumination mode will interfere with the desired measurement signals.

[0042] As shown in Figure 3(b), target T is placed with substrate W normal to the optical axis O of objective lens 16. The substrate W may be supported by a support (not shown). A ray of measurement radiation I impinging on target T from an angle off the axis O gives rise to a zeroth order ray (solid line 0) and two first order rays (dot-chain line +1 and double dot-chain line -1). It should be remembered that with an overfilled small target, these rays are just one of many parallel rays covering the area of the substrate including metrology target T and other features. Since the aperture in plate 13 has a finite width (necessary to admit a useful quantity of light, the incident rays I will in fact occupy a range of angles, and the diffracted rays 0 and +1 / -1 will be spread out somewhat. According to the point spread function of a small target, each order +1 and -1 will be further spread over a range of angles, not a single ideal ray as shown. Note that the grating pitches of the targets and the illumination angles can be designed or adjusted so that the first order rays entering the objective lens are closely aligned with the central optical axis. The rays illustrated in Figure 3(a) and 3(b) are shown somewhat off axis, purely to enable them to be more easily distinguished in the diagram.

[0043] At least the 0 and +1 orders diffracted by the target T on substrate W are collected by objective lens 16 and directed back through beam splitter 15. Returning to Figure 3(a), both the first and second illumination modes are illustrated, by designating diametrically opposite apertures labeled as north (N) and south (S). When the incident ray I of measurement radiation is from the north side of the optical axis, that is when the first illumination mode is applied using aperture plate 13N, the +1 diffracted rays, which are labeled +I(N), enter the objective lens 16. In contrast, when the secondillumination mode is applied using aperture plate 13S the -1 diffracted rays (labeled 1(S)) are the ones which enter the lens 16.

[0044] A second beam splitter 17 divides the diffracted beams into two measurement branches. In a first measurement branch, optical system 18 forms a diffraction spectrum (pupil plane image) of the target on first sensor 19 (e.g. a CCD or CMOS sensor) using the zeroth and first order diffractive beams. Each diffraction order hits a different point on the sensor, so that image processing can compare and contrast orders. The pupil plane image captured by sensor 19 can be used for focusing the metrology apparatus and / or normalizing intensity measurements of the first order beam. The pupil plane image can also be used for many measurement purposes such as reconstruction.

[0045] In the second measurement branch, optical system 20, 22 forms an image of the target T on sensor 23 (e.g. a CCD or CMOS sensor). In the second measurement branch, an aperture stop 21 is provided in a plane that is conjugate to the pupil-plane. Aperture stop 21 functions to block the zeroth order diffracted beam so that the image of the target formed on sensor 23 is formed only from the -1 or +1 first order beam. The images captured by sensors 19 and 23 are output to processor PU which processes the image, the function of which will depend on the particular type of measurements being performed. Note that the term ‘image’ is used here in a broad sense. An image of the grating lines as such will not be formed, if only one of the -1 and +1 orders is present.

[0046] The particular forms of aperture plate 13 and field stop 21 shown in Figure 3 are purely examples. In another embodiment of the invention, on-axis illumination of the targets is used and an aperture stop with an off-axis aperture is used to pass substantially only one first order of diffracted light to the sensor. In yet other embodiments, 2nd, 3rd and higher order beams (not shown in Figure 3) can be used in measurements, instead of or in addition to the first order beams.

[0047] In order to make the measurement radiation adaptable to these different types of measurement, the aperture plate 13 may comprise a number of aperture patterns formed around a disc, which rotates to bring a desired pattern into place. Note that aperture plate 13N or 13S can only be used to measure gratings oriented in one direction (X or Y depending on the set-up). For measurement of an orthogonal grating, rotation of the target through 90° and 270° might be implemented.

[0048] There are many actions and events which may typically prompt the performance of an exposure apparatus qualification action. For example, such a qualification may be performed prior to or as part of installing an exposure apparatus at a site or fabrication plant and / or subsequently to performance of a maintenance action. Such a maintenance action may comprise, for example, replacement of a hardware component which is subject to degradation over time (e.g., replacement of a wafer table or projection lens) or replacement or update of a software module. Exposure apparatus qualification may also be performed when developing new products (e.g., hardware and / or software modules).

[0049] At a system level, such a qualification action may measure the final performance of the exposure apparatus in terms of system -level performance parameters. These system -level performanceparameters may comprise productivity performance (e.g., relating to productivity or speed) and a number of quality performance parameters, namely: focus performance, imaging performance, defectivity performance and overlay performance.

[0050] Standard qualification tests such as for overlay (e g., a Dedicated Chuck Overlay (DCO) test) are not application specific and therefore are not representative of on-product performance.

[0051] As such, an improved method for qualifying actual on-product performance of exposure apparatuses (e.g., lithography apparatuses) is desirable. Such a qualification may assess whether the contribution to on-product performance attributable to the lithography apparatus is acceptable, thereby minimizing or preventing yield loss during production.

[0052] A customized Dedicated Chuck Overlay (CDCO) test has been devised, which is an improved overlay qualification test designed to assess on-product overlay performance. It achieves this by including application dependent contributions such as lens heating, reticle heating, wafer heating and illumination dependencies, when exposed at (e.g., close to) maximum throughput (i.e., such that these heat loads etc. are maximized and / or close to saturation.

[0053] However, overlay is only a single measure of performance, and yield is dependent on other metrics in addition to overlay. A better metric, therefore, is edge placement error (EPE), which is a local metric which describes the relative displacement of the edges of features from their intended target location. EPE is a combination of overlay errors, CD errors and stochastics (e.g., line width roughness or line edge roughness).

[0054] EPE can be measured directly using metrology tools such as a scanning electron microscope or e-beam tool. However, this is typically not possible or practical for qualification, e.g., due to the time (multiple days) involved to perform a comprehensive SEM measurement over a substrate.

[0055] A formula for EPE has been devised, which potentially enables EPE to be estimated from various metrology data such as overlay data, CD data and stochastic data such as line edge roughness LER or line width roughness LWR. Because such data is generated from the various qualification tests presently performed, it may seem intuitive that presently generated qualification test data may be used to perform a qualification test based on such a calculated EPE metric.

[0056] However, each of the present qualification tests are performed individually, and typically in each case performed with different use-case conditions / settings (e.g. dose) and at different moments in time. As such environmental and other conditions of the will not be the same. It can be appreciated that EPE is the combined result of the overlay and imaging performance from the same exposure, implying the same use-case and system conditions. In addition, the non-common measurement layout of the different qualification tests means that the different tests measure performance at different positions on the reticle and wafer, whereas EPE addresses performance at the same position. Because of this, calculating an EPE value from disparate qualification test data from different tests / times / settings will yield an inaccurate and largely non-representative estimate of EPE.

[0057] To address these issues, an improved qualification test is proposed which uses a new qualification reticle to expose at least one qualification substrate. The qualification reticle may comprise representative product features to form representative (e.g., dummy) product structure which is representative of actual product structure for a particular application (e.g., for a particular product or product type being exposed). The qualification reticle may further comprise one or more sets of metrology features for forming corresponding sets of metrology structures, said set of metrology structures comprising metrology structures for measuring two or more parameters related to edge placement error or any other local structure placement metric describing local placement of a feature and / or edge thereof.

[0058] The majority of the reticle area of the qualification reticle may comprise the representative product features may, so as to substantially mimic an actual product reticle. For example, more than 60%, more than 70%, more than 80%, more than 90%, more than 95% or more than 97% of the (e.g., active) reticle area may comprise representative product features. The sets of metrology features may therefore cover a relatively small proportion of the reticle area, e.g., so as to minimize impact on the diffraction behavior of the product feature.

[0059] The qualification reticle may comprise a plurality of said sets of metrology features; e.g., where each set of metrology features is comprised within a “metrology module”. Each metrology module and / or set of metrology features may be (at least partially) surrounded by the representative product structure features, such that, on the qualification substrate, each set of metrology structures are (at least partially) surrounded by the representative product structure.

[0060] The metrology features may be such that, on the qualification substrate, each set of metrology structures (e.g., metrology targets) comprise at least overlay structures (overlay targets) and imaging structures (imaging targets). Optionally each set of metrology structures may comprise focus structures (focus targets) and / or metrology structures for measuring any other parameter or metric which may be of interest for assessing performance and / or diagnostics in qualification.

[0061] Optionally, the at least overlay features and the at least imaging features may be comprised within a dual feature type or target type which form corresponding dual metrology structures on the qualification substrate. Such dual metrology structures may comprise single structure s / targets which can be measured to determine both overlay and at least one imaging parameter. Similarly other combined targets may be envisaged, such as dual overlay and focus metrology targets, dual imaging and focus metrology targets or even a metrology target from which overlay, focus and the imaging parameter can all be measured.

[0062] Each set of metrology features may be comprised within a small region on the reticle (and therefore on the substrate when exposed), such that when exposed onto the substrate, they will have reacted in substantially the same way to any performance disturbance at reticle level and / or substrate level, which is important for determining EPE. For example, the area occupied by each set of metrology features (each metrology module or a portion thereof comprising the metrology features)may be less than 10mm, less than 8mm, less than 6mm, less than 5mm, less than 4mm, less than 3.5mm, less than 3mm, less than 2mm, less than 1mm or less than 0.5mm on the reticle in each of the X and Y directions of the reticle plane (i.e., a plane substantially parallel to the substrate plane). Taking into account the projection system magnification, this means that the area occupied by each set of metrology structures on the substrate will not extend further than a distance between 2.5mm (10mm / 4) and 0.125mm (0.5mm / 4) in each of the X and Y directions of the substrate plane.

[0063] For each of said one or more sets of metrology features, at least one of said one or more overlay features is, on the reticle, within 10mm, within 8mm, within 6mm, within 5mm, within 4mm, within 3.5mm, within 3mm, within 2mm, within 1mm or within 0.5mm of at least one of said one or more imaging features. Therefore, the corresponding overlay and imaging structures will be within 0.25x each of these example distances on the qualification substrate. Optionally, where each set (or at least some of said sets) of metrology features comprises a plurality of overlay features and a plurality of imaging features, then the largest distance between one of the overlay features and one of the imaging features per set of metrology features may be less than 10mm, less than 8mm, less than 6mm, less than 5mm, less than 4mm, less than 3.5mm, less than 3mm, less than 2mm, less than 1mm or less than 0.5mm on the reticle. Again, the corresponding largest distance on the qualification substrate will be 0.25x each of these example distances.

[0064] The reticle may comprise, for example, more than 30, more than 40, more than 50, more than 60, more than 70, more than 80, or more than 90 sets of metrology features (metrology modules). The sets of metrology features may be substantially evenly spaced on the reticle, e.g., in a regular 2D grid arrangement. Each set of metrology features may be at least partially surrounded by representative product structure features.

[0065] A qualification exposure step may comprise exposing at least one qualification substrate with the qualification reticle. The qualification exposure step may expose substantially the entire substrate surface using the qualification reticle; e.g., the number of exposed fields may comprise more than 50, more than 60, more than 70, more than 80, or more than 85. In this way, the exposed qualification substrate may comprise more than 5000 sets of metrology marks, more than 6000 sets of metrology marks or more than 7000 sets of metrology marks (taking into account some partial edge fields).

[0066] A metrology step may measure the qualification substrate(s) using one or more suitable metrology tools. The metrology tools used may depend on the metrology structures exposed on the substrate. For example, for overlay, the overlay structures may comprise micro-diffraction based overlay (pDBO) targets which comprise an overlay dependent asymmetry. Such pDBO targets are well known and will not be described in great detail. Briefly, they comprise a periodic structure or grating in each of the layers for which overlay is being measured (overlay being a relative displacement between layers). Different sub-targets or pads may measure overlay in each of the two substrate plane dimensions. Two sub-targets per direction may be provided per target, each with a different deliberate bias so as to help separate the overlay dependent asymmetries from other nuisancetarget asymmetries. Such pDBO targets may be measured using a scatterometer based metrology apparatus; e.g., a metrology apparatus such as illustrated in Figure 3(a). However, it can be appreciated that pDBO is only one overlay target type and other overlay target types may be provided, either as an alternative or in addition to pDBO targets. Such other overlay target types may be measurable using a scatterometer based metrology apparatus and / or any other type of metrology apparatus depending on the target type.

[0067] The imaging structures may comprise any structure measurable using, e.g., a scatterometer based metrology apparatus such as, for example, illustrated in Figure 3(a). Such metrology apparatuses may measure the linewidth (CD) of e.g., simple line-space metrology structures (e.g., in each layer for which imaging is being assessed). Again, the imaging structures may be provided for each of the two directions of the substrate plane. Any suitable metrology method and apparatus for measuring CD and / or CD uniformity (CDU) may be used. Once again, the type of imaging structure may differ from that described here.

[0068] The method may further comprise measuring stochastic imaging parameter such as LWR or LER, e.g., from one or both of the imaging structure and the overlay structure. This can be achieved using any suitable technique and any suitable metrology apparatus for measuring LWR / LER. For example, the metrology apparatus may comprise an apparatus having sufficient resolution to measure a local parameter such as LWR / LER, e.g., an electron microscope (scanning or transmission) or e- beam apparatus (itself a form of SEM).

[0069] Where provided, focus structures may comprise micro-diffraction based focus (pDBF) targets which comprise a focus dependent asymmetry (e.g., by the provision of assist features below the resolution of the lithographic apparatus which do not print, but affect the formation of the line feature in a focus dependent manner). Such uDBF targets are well known and will not be described in great detail. Briefly, they comprise a periodic structure in each layer for which focus is being measured (focus in this context describes the exposure focus when exposing the focus structure). Different subtargets or pads may measure the effect of focus in each of the two substrate plane dimensions. Such pDBF targets may be measured using a scatterometer based metrology apparatus; e.g., a metrology apparatus such as illustrated in Figure 3(a). However, it can be appreciated that uDBF is only one focus target type and other focus target types may be provided, either as an alternative or in addition to pDBF targets. Such other focus target types may be measurable using a scatterometer based metrology apparatus and / or any other type of metrology apparatus depending on the target type.

[0070] In principle, any structure type(s) can be chosen dependent on the use-case that is considered relevant for the system performance qualification and any test protocol used for the qualification.

[0071] The qualification data obtained in the metrology step may be assessed, e g., with respect to one or more target performance criteria, to determine if the on-product performance of the lithographic apparatus is acceptable for the particular application for which it is being qualified (e.g., for exposing product for which said representative structures represent). This assessment maycomprise determining local structure placement metric data (e.g., EPE data) from the qualification data. Such a method may determine the local structure placement metric data using an equation which equates the local structure placement metric to an overlay metric, a critical dimension metric (e.g., CDU) and a structure roughness metric (e g., LER and / or LWR). As such, the local structure placement metric data can be determined from overlay qualification data and an imaging qualification data (e.g., qualification CDU imaging data and qualification LWR / LER imaging data)

[0072] Different formulae have been devised for estimating a feature placement metric such as EPE from diverse test data, and any such formula may be used. One example is shown below:

[0073] where EPEsysis the systematic EPE component which can be determined per lithographic apparatus and / or reticle, o0VLis the overlay error (global error) as described by the overlay qualification data, CTCDU is the CDU error (global error) as described by or at least one component of the imaging qualification data and C?LWR is the line width roughness (local error due to stochastic effects), described by another component of the imaging qualification data. The effect on EPE of local errors may be approximately equal to the effect of the global errors.

[0074] Because each term of this equation relates to the same exposures on a single qualification substrate (or set of qualification substrates), the determined EPE will be a valid estimate of the EPE on the substrate.

[0075] Figure 4 illustrates an example qualification reticle 400 which may be used in qualification testing according to the concepts disclosed herein. The qualification reticle 400 comprises multiple representative structure areas 405 comprising representative structure features and metrology modules 410 comprising sets of metrology features. To separate different representative structure areas 405, there may be provided transparent pad areas 415. The transparent pad areas 415 provide open area to match the reticle transmission to the particular application / use-case. The metrology modules 410 may be arranged on a substantially regular grid (here a 13x7 grid, purely as an example). The representative structure may be representative of, and arranged similar to, actual product for a particular application or use case (e.g., a particular product to be exposed using the lithographic apparatus).

[0076] A detail of an example metrology module 410 is shown below the qualification reticle 400. The metrology module comprises an (or at least one) overlay structure area 425 comprising overlay features 445, and an (or at least one) imaging structure area 420 comprising imaging features 440 (optionally these may be combined within a single feature). Optionally, the metrology module 410 may comprise at least one focus structure area 430 comprising focus features 450. Also optionally, themetrology module may comprise one or more other metrology structure and / or diagnostic structure areas 435 comprising different feature types. The arrangement of these different areas may vary from shown, e.g., they may extend only over a sub-area of the metrology module area (e.g., they may all be comprised within a half, a third, a quarter, a fifth or a sixth of the metrology module area) and / or may be ordered / arranged differently from illustrated. The remaining metrology module area may optionally comprise, for example, one or more absorber areas (not shown).

[0077] Some or all of the metrology feature s / structures may be “product-like”; e.g., comprise a CD which is similar (e.g., within 20%, within 10% or within 5%) of the (e.g., average) product CD of the product for which the lithographic apparatus is being qualified for. Different CD variants (e.g., CD widths) of product features may be included on the reticle to ensure that the structures printed onto wafer have their width close to target CDs. The CD variants may be based on simulation, which may be tuned with experiment data.

[0078] As is demonstrated by the above provided equation example for EPE, focus performance is not directly needed to assess EPE performance. However, overlay and imaging performance is sensitive to focus performance. Hence, focus performance indirectly contributes to EPE. Focus features may therefore be included in the proposed qualification reticle design for diagnostic purposes, e.g., to make troubleshooting more efficient. For example, should the overlay and / or imaging qualification data be indicative of poor performance, the focus qualification data may provide useful diagnostic information to help diagnose a reason for the poor performance. The other metrology structures may provide additional diagnostic information in addition.

[0079] By using a qualification reticle comprising different product-like metrology features enables system performance qualification where the relevant overlay, imaging and focus qualification data can be collected from a single test execution. This addresses the issue of exposing individual qualification tests with different use-case conditions and different system conditions such as environmental temperatures, pressures and / or humidity.

[0080] The combination of the above qualification data enables the verification of EPE predictions using in-resist measurement data, and can be done prior to shipping a first lithography system. This creates an opportunity to proactively identify and address potential yield issues in an improved manner which takes into account particular application cases.

[0081] This multi-competence qualification could be added to the standard qualification process or even replace part of the standard qualification place since it would cover system performance qualification in terms of overlay, imaging and focus (which are separately qualified presently).

[0082] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.Other aspects of the invention are set out in the following numbered clauses:1. A method of performing a qualification action relating to an exposure apparatus, the method comprising:using the exposure apparatus to expose a qualification patterning device onto at least one qualification substrate, the qualification patterning device comprising one or more sets of metrology features, each of said one or more sets of metrology features for forming a respective set of metrology structures on the qualification substrate, the one or more sets of metrology features comprising one or more overlay features for forming one or more overlay structures on the qualification substrate for the measurement of overlay and one or more imaging features for forming one or more imaging structures on the qualification substrate for the measurement of at least one imaging parameter, wherein, for each of the one or more sets of metrology structures, at least one of said one or more overlay structures is, on the qualification substrate, within 2.5mm of at least one of said one or more imaging structures; measuring the at least one qualification substrate to obtain qualification data comprising at least overlay qualification data relating to overlay and imaging qualification data relating to the at least one imaging parameter; determining at least one local structure placement metric from said at least overlay qualification data and imaging qualification data; and qualifying said exposure apparatus by assessing said local structure placement metric.2. A method as set out in clause 1, wherein said imaging qualification data relates to at least a critical dimension parameter of said imaging structures.3. A method as set out in clause 2, wherein said critical dimension parameter comprises critical dimension uniformity.4. A method as set out in any preceding clause, wherein said imaging qualification data comprises stochastic imaging data relating to a stochastic imaging parameter.5. A method as set out in clause 4, wherein the stochastic imaging parameter comprises line edge roughness and / or line width roughness.6. A method as set out in any preceding clause, wherein said local structure placement metric comprises edge placement error.7. A method as set out in any preceding clause, wherein said local structure placement metric is determined via a function dependent on overlay metric, a critical dimension metric and a structure roughness metric.8. A method as set out in any preceding clause, wherein said qualification patterning device comprises a plurality of said sets of metrology features, each set of metrology features comprising a respective at least one overlay feature and a respective at least one imaging feature.9. A method as set out in any preceding clause, wherein each set of metrology features comprises at least one focus feature for forming at least one focus structure on the qualification substrate for the measurement of focus.10. A method as set out in clause 9, wherein said measuring step comprises measuring the focus structures to obtain focus qualification data; and using the focus qualification data to diagnose any issues identified in the qualification step.11. A method as set out in any preceding clause, wherein said qualification patterning device comprises representative product features, for forming representative product structures being representative of product structures of a particular application and / or use case for said exposure apparatus.12. A method as set out in clause 11, wherein each set of measurement features is at least partially surrounded by said representative product features.13. A method as set out in clause 11 or 12, wherein each said set of metrology features comprises a critical dimension which is within 20% of a critical dimension of the representative product structures.14. A method as set out in any of the clauses 11 to 13, wherein said representative product features are comprised over 70% of the patterning area of the qualification patterning device.15. A method as set out in any of the clauses 11 to 13, wherein said representative product features are comprised over 90% of the patterning area of the qualification patterning device16. A method as set out in any preceding clause, wherein said one or more overlay features and said one or more imaging features are realized as one or more combined overlay and imaging features for forming one or more combined overlay and imaging structures on the qualification substrate for the measurement of overlay and said imaging parameter.17. A method as set out in any preceding clause, wherein an area occupied on the qualification substrate by each at least one set of metrology structures is no larger than 2.5mm in each of two mutually perpendicular directions of a substrate plane defined by the qualification substrate.18. A method as set out in any preceding clause, wherein an area occupied on the qualification substrate by each at least one set of metrology structures is no larger than 1 ,25mm in each of two mutually perpendicular directions of a substrate plane defined by the qualification substrate.19. A method as set out in any preceding clause, wherein an area occupied on the qualification substrate by each at least one set of metrology structures is no larger than 0.75mm in each of two mutually perpendicular directions of a substrate plane defined by the qualification substrate.20. A method as set out in any preceding clause, wherein an area occupied on the qualification substrate by each at least one set of metrology structures is no larger than 0.25mm in each of two mutually perpendicular directions of a substrate plane defined by the qualification substrate.21. A method as set out in any preceding clause, wherein, for each of the one or more sets of metrology structures, at least one of said one or more overlay structures is, on the qualification substrate, within 1.25mm of at least one of said one or more imaging structures.22. A method as set out in any preceding clause, wherein, for each of the one or more sets of metrology structures, at least one of said one or more overlay structures is, on the qualification substrate, within 0.75mm of at least one of said one or more imaging structures.23. A method as set out in any preceding clause, wherein, for each of the one or more sets of metrology structures, at least one of said one or more overlay structures is, on the qualification substrate, within 0.25mm of at least one of said one or more imaging structures.24. A method as set out in any preceding clause, wherein said qualification patterning device comprises more than 50 said sets of metrology features.25. A method as set out in any preceding clause, wherein said qualification patterning device comprises more than 70 said sets of metrology features.26. A method as set out in any preceding clause, wherein said qualification patterning device comprises more than 90 said sets of metrology features.27. A method as set out in any preceding clause, wherein said measuring the at least one qualification substrate comprises using a scatterometer to measure at least overlay structures.28. A method as set out in any preceding clause, wherein said measuring the at least one qualification substrate comprises using a scatterometer to measure at least imaging structures.29. A method as set out in any preceding clause, wherein the expose step comprises exposing said qualification patterning device over a plurality of exposure fields substantially covering the entire qualification substrate.30. A computer program comprising program instructions operable to perform the method of any preceding clause, when run on a suitable apparatus.31. A non-transient computer program carrier comprising the computer program of clause 30.32. A processing arrangement comprising: a non-transient computer program carrier comprising a computer program comprising program instructions operable to perform the method of any of clauses 1 to 29, when run on a suitable apparatus; and a processor operable to run the computer program comprised on said non-transient computer program carrier.33. An exposure apparatus comprising the processing arrangement of clause 32.34. An exposure apparatus as claimed in clause 33, said exposure apparatus comprising a lithographic apparatus.35. A qualification patterning device for qualifying an exposure apparatus, comprising: a plurality of sets of metrology features, each of the plurality of sets of metrology features comprising one or more overlay features for forming one or more overlay structures on the qualification substrate for the measurement of overlay and one or more imaging features for forming one or more imaging structures on the qualification substrate for the measurement of at least one imaging parameter, wherein, for each of said one or more sets of metrology features, at least one of said one or more overlay features is, on the reticle, within 10mm of at least one of said one or more imaging features; andrepresentative product features for forming representative product structures being representative of product structures of a particular application and / or use case for said exposure apparatus.36. A qualification patterning device as set out in clause 35, wherein each set of metrology features comprises at least one focus feature for forming at least one focus structure on the qualification substrate for the measurement of focus.37. A qualification patterning device as set out in clause 35 or 36, wherein each set of measurement features is at least partially surrounded by said representative product features.38. A qualification patterning device as set out in clause 35, 36 or 37, wherein each said set of metrology features comprises a critical dimension which is within 20% of a critical dimension of the representative product structures.39. A qualification patterning device as set out in any of clauses 35 to 38, wherein said one or more overlay features and said one or more imaging features are realized as one or more combined overlay and imaging features for forming one or more combined overlay and imaging structures on the qualification substrate for the measurement of overlay and said imaging parameter.40. A qualification patterning device as set out in any of clauses 35 to 39, wherein an area occupied on the qualification patterning device by each at least one set of metrology features is no larger than 10mm in each of two mutually perpendicular directions of a qualification patterning device plane defined by the qualification patterning device surface.41. A qualification patterning device as set out in any of clauses 35 to 39, wherein an area occupied on the qualification patterning device by each at least one set of metrology features is no larger than 5mm in each of two mutually perpendicular directions of a qualification patterning device plane defined by the qualification patterning device surface.42. A qualification patterning device as set out in any of clauses 35 to 39, wherein an area occupied on the qualification patterning device by each at least one set of metrology features is no larger than 3mm in each of two mutually perpendicular directions of a qualification patterning device plane defined by the qualification patterning device surface.43. A qualification patterning device as set out in any of clauses 35 to 39, wherein an area occupied on the qualification patterning device by each at least one set of metrology features is no larger than 1mm in each of two mutually perpendicular directions of a qualification patterning device plane defined by the qualification patterning device surface.44. A qualification patterning device as set out in any of clauses 35 to 43, wherein, for each of said one or more sets of metrology features, at least one of said one or more overlay features is, on the reticle, within 5mm of at least one of said one or more imaging features.45. A qualification patterning device as set out in any of clauses 35 to 43, wherein, for each of said one or more sets of metrology features, at least one of said one or more overlay features is, on the reticle, within 3mm of at least one of said one or more imaging features.46. A qualification patterning device as set out in any of clauses 35 to 43, wherein, for each of said one or more sets of metrology features, at least one of said one or more overlay features is, on the reticle, within 1mm of at least one of said one or more imaging features.47. A qualification patterning device as set out in any of clauses 35 to 46, wherein said qualification patterning device comprises more than 50 said sets of metrology features.48. A qualification patterning device as set out in any of clauses 35 to 46, wherein said qualification patterning device comprises more than 70 said sets of metrology features.49. A qualification patterning device as set out in any of clauses 35 to 46, wherein said qualification patterning device comprises more than 90 said sets of metrology features.50. A qualification patterning device as set out in any of clauses 35 to 49, wherein said representative product features are comprised over 70% of the patterning area of the qualification patterning device.51. A qualification patterning device as set out in any of clauses 35 to 49, wherein said representative product features are comprised over 90% of the patterning area of the qualification patterning device.52. A qualification substrate obtained by exposing the qualification patterning device as set out in any of clauses 35 to 51 over a plurality of exposure fields substantially covering the entire qualification substrate.

[0083] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

[0084] The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g., having a wavelength in the range of 1-100 nm), as well as particle beams, such as ion beams or electron beams.

[0085] The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components. Reflective components are likely to be used in an apparatus operating in the UV and / or EUV ranges.

[0086] The breadth and scope of the present invention should not be limited by any of the abovedescribed exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

CLAIMS1. A method of performing a qualification action relating to an exposure apparatus, the method comprising: using the exposure apparatus to expose a qualification patterning device onto at least one qualification substrate, the qualification patterning device comprising one or more sets of metrology features, each of said one or more sets of metrology features for forming a respective set of metrology structures on the qualification substrate, the one or more sets of metrology features comprising one or more overlay features for forming one or more overlay structures on the qualification substrate for the measurement of overlay and one or more imaging features for forming one or more imaging structures on the qualification substrate for the measurement of at least one imaging parameter, wherein, for each of the one or more sets of metrology structures, at least one of said one or more overlay structures is, on the qualification substrate, within 2.5mm of at least one of said one or more imaging structures; measuring the at least one qualification substrate to obtain qualification data comprising at least overlay qualification data relating to overlay and imaging qualification data relating to the at least one imaging parameter; determining at least one local structure placement metric from said at least overlay qualification data and imaging qualification data; and qualifying said exposure apparatus by assessing said local structure placement metric.

2. A method as claimed in claim 1, wherein said imaging qualification data relates to at least a critical dimension parameter of said imaging structures.

3. A method as claimed in claim 1 or 2, wherein said local structure placement metric is determined via a function dependent on overlay metric, a critical dimension metric and a structure roughness metric.

4. A method as claimed in any preceding claim, wherein said qualification patterning device comprises a plurality of said sets of metrology features, each set of metrology features comprising a respective at least one overlay feature and a respective at least one imaging feature. . A method as claimed in any preceding claim, wherein said qualification patterning device comprises representative product features, for forming representative product structures being representative of product structures of a particular application and / or use case for said exposure apparatus.

6. A method as claimed in claim 5, wherein each set of measurement features is at least partially surrounded by said representative product features.

7. A method as claimed in any preceding claim, wherein said one or more overlay features and said one or more imaging features are realized as one or more combined overlay and imaging features for forming one or more combined overlay and imaging structures on the qualification substrate for the measurement of overlay and said imaging parameter.

8. A computer program comprising program instructions operable to perform the method of any preceding claim, when run on a suitable apparatus.

9. A non-transient computer program carrier comprising the computer program of claim 8.

10. A processing arrangement comprising : a non-transient computer program carrier comprising a computer program comprising program instructions operable to perform the method of any of claims 1 to 7, when run on a suitable apparatus; and a processor operable to run the computer program comprised on said non-transient computer program carrier.

11. An exposure apparatus comprising the processing arrangement of claim 10.

12. A qualification patterning device for qualifying an exposure apparatus, comprising: a plurality of sets of metrology features, each of the plurality of sets of metrology features comprising one or more overlay features for forming one or more overlay structures on the qualification substrate for the measurement of overlay and one or more imaging features for forming one or more imaging structures on the qualification substrate for the measurement of at least one imaging parameter, wherein, for each of said one or more sets of metrology features, at least one of said one or more overlay features is, on the reticle, within 10mm of at least one of said one or more imaging features; and representative product features for forming representative product structures being representative of product structures of a particular application and / or use case for said exposure apparatus.

13. A qualification patterning device as claimed in claim 12, wherein each set of metrology features comprises at least one focus feature for forming at least one focus structure on the qualification substrate for the measurement of focus.

14. A qualification patterning device as claimed in claim 12 or 13, wherein each set of measurement features is at least partially surrounded by said representative product features.

15. A qualification patterning device as claimed in any of claims 12 to 14, wherein said one or more overlay features and said one or more imaging features are realized as one or more combined overlay and imaging features for forming one or more combined overlay and imaging structures on the qualification substrate for the measurement of overlay and said imaging parameter.

16. A qualification substrate obtained by exposing the qualification patterning device as claimed in any of claims 12 to 15 over a plurality of exposure fields substantially covering the entire qualification substrate.

Images